/*
 * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE
 * file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file
 * to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the
 * License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */
package com.blade.mvc.multipart;

import java.io.*;

/**
 * <p>
 * Low level API for processing file uploads.
 * <p>
 * <p>
 * This class can be used to process data streams conforming to MIME 'multipart' format as defined in <a
 * href="http://www.ietf.org/rfc/rfc1867.txt">RFC 1867</a>. Arbitrarily large amounts of data in the stream can be
 * processed under constant memory usage.
 * <p>
 * <p>
 * The format of the stream is defined in the following way:<br>
 * <p>
 * <code>
 * multipart-body := preamble 1*encapsulation close-delimiter epilogue<br>
 * encapsulation := delimiter body CRLF<br>
 * delimiter := "--" boundary CRLF<br>
 * close-delimiter := "--" boudary "--"<br>
 * preamble := &lt;ignore&gt;<br>
 * epilogue := &lt;ignore&gt;<br>
 * body := header-part CRLF body-part<br>
 * header-part := 1*header CRLF<br>
 * header := header-name ":" header-value<br>
 * header-name := &lt;printable ascii characters except ":"&gt;<br>
 * header-value := &lt;any ascii characters except CR &amp; LF&gt;<br>
 * body-data := &lt;arbitrary data&gt;<br>
 * </code>
 * <p>
 * <p>
 * Note that body-data can contain another mulipart entity. There is limited support for single pass processing of such
 * nested streams. The nested stream is <strong>required</strong> to have a boundary token of the same length as the
 * parent stream (see {@link #setBoundary(byte[])}).
 * <p>
 * <p>
 * Here is an example of usage of this class.<br>
 * <p>
 * <pre>
 * try {
 * 	MultipartStream multipartStream = new MultipartStream(input, boundary);
 * 	boolean nextPart = multipartStream.skipPreamble();
 * 	OutputStream output;
 * 	while (nextPart) {
 * 		String header = multipartStream.readHeaders();
 * 		// process headers
 * 		// create some output stream
 * 		multipartStream.readBodyData(output);
 * 		nextPart = multipartStream.readBoundary();
 *    }
 * } catch (MultipartStream.MalformedStreamException e) {
 * 	// the stream failed to follow required syntax
 * } catch (IOException e) {
 * 	// a read or write error occurred
 * }
 * </pre>
 *
 * @author <a href="mailto:Rafal.Krzewski@e-point.pl">Rafal Krzewski</a>
 * @author <a href="mailto:martinc@apache.org">Martin Cooper</a>
 * @author Sean C. Sullivan
 * @version $Id: MultipartStream.java 735374 2009-01-18 02:18:45Z jochen $
 */
public class MultipartReader {

    /**
     * The Carriage Return ASCII character value.
     */
    public static final byte CR = 0x0D;

    /**
     * The Line Feed ASCII character value.
     */
    public static final byte LF = 0x0A;

    /**
     * The dash (-) ASCII character value.
     */
    public static final byte DASH = 0x2D;

    /**
     * The maximum length of <code>header-part</code> that will be processed (10 kilobytes = 10240 bytes.).
     */
    public static final int HEADER_PART_SIZE_MAX = 10240;

    /**
     * The default length of the buffer used for processing a request.
     */
    protected static final int DEFAULT_BUFSIZE = 4096;

    /**
     * A byte sequence that marks the end of <code>header-part</code> (<code>CRLFCRLF</code>).
     */
    protected static final byte[] HEADER_SEPARATOR = {CR, LF, CR, LF};

    /**
     * A byte sequence that that follows a delimiter that will be followed by an encapsulation (<code>CRLF</code>).
     */
    protected static final byte[] FIELD_SEPARATOR = {CR, LF};

    /**
     * A byte sequence that that follows a delimiter of the last encapsulation in the stream (<code>--</code>).
     */
    protected static final byte[] STREAM_TERMINATOR = {DASH, DASH};

    /**
     * A byte sequence that precedes a boundary (<code>CRLF--</code>).
     */
    protected static final byte[] BOUNDARY_PREFIX = {CR, LF, DASH, DASH};

    /**
     * The input stream from which data is read.
     */
    private final InputStream input;

    /**
     * The length of the boundary token plus the leading <code>CRLF--</code>.
     */
    private int boundaryLength;

    /**
     * The amount of data, in bytes, that must be kept in the buffer in order to detect delimiters reliably.
     */
    private int keepRegion;

    /**
     * The byte sequence that partitions the stream.
     */
    private byte[] boundary;

    /**
     * The length of the buffer used for processing the request.
     */
    private final int bufSize;

    /**
     * The buffer used for processing the request.
     */
    private final byte[] buffer;

    /**
     * The index of first valid character in the buffer.<br>
     * 0 <= head < bufSize
     */
    private int head;

    /**
     * The index of last valid characer in the buffer + 1.<br>
     * 0 <= tail <= bufSize
     */
    private int tail;

    /**
     * The content encoding to use when reading headers.
     */
    private String headerEncoding;

    /**
     * <p>
     * Constructs a <code>MultipartStream</code> with a custom size buffer.
     * <p>
     * <p>
     * Note that the buffer must be at least big enough to contain the boundary string, plus 4 characters for CR/LF and
     * double dash, plus at least one byte of data. Too small a buffer size setting will degrade performance.
     *
     * @param input    The <code>InputStream</code> to serve as a data source.
     * @param boundary The token used for dividing the stream into <code>encapsulations</code>.
     * @param bufSize  The size of the buffer to be used, in bytes.
     */
    public MultipartReader(InputStream input, byte[] boundary, int bufSize) {
        this.input = input;
        this.bufSize = bufSize;
        this.buffer = new byte[bufSize];

        // prepend CR/LF to the boundary to chop trailing CR/LF from body-data tokens.
        this.boundary = new byte[boundary.length + BOUNDARY_PREFIX.length];
        this.boundaryLength = boundary.length + BOUNDARY_PREFIX.length;
        this.keepRegion = this.boundary.length;
        System.arraycopy(BOUNDARY_PREFIX, 0, this.boundary, 0, BOUNDARY_PREFIX.length);
        System.arraycopy(boundary, 0, this.boundary, BOUNDARY_PREFIX.length, boundary.length);

        head = 0;
        tail = 0;
    }

    /**
     * Constructs a <code>MultipartStream</code> with a default size buffer.
     *
     * @param input    The <code>InputStream</code> to serve as a data source.
     * @param boundary The token used for dividing the stream into <code>encapsulations</code>.
     */
    public MultipartReader(InputStream input, byte[] boundary) {
        this(input, boundary, DEFAULT_BUFSIZE);
    }

    /**
     * Retrieves the character encoding used when reading the headers of an individual part. When not specified, or
     * <code>null</code>, the platform default encoding is used.
     *
     * @return The encoding used to read part headers.
     */
    public String getHeaderEncoding() {
        return headerEncoding;
    }

    /**
     * Specifies the character encoding to be used when reading the headers of individual parts. When not specified, or
     * <code>null</code>, the platform default encoding is used.
     *
     * @param encoding The encoding used to read part headers.
     */
    public void setHeaderEncoding(String encoding) {
        headerEncoding = encoding;
    }

    /**
     * Reads a byte from the <code>buffer</code>, and refills it as necessary.
     *
     * @return The next byte from the input stream.
     * @throws IOException if there is no more data available.
     */
    public byte readByte() throws IOException {

        // buffer depleted ?
        if (head == tail) {
            head = 0;
            // Refill.
            tail = input.read(buffer, head, bufSize);
            if (tail == -1) {
                // no more data available.
                throw new IOException("No more data is available");
            }
        }

        return buffer[head++];
    }

    /**
     * Skips a <code>boundary</code> token, and checks whether more <code>encapsulations</code> are contained in the
     * stream.
     *
     * @return <code>true</code> if there are more encapsulations in this stream; <code>false</code> otherwise.
     * @throws MalformedStreamException if the stream ends unexpecetedly or fails to follow required syntax.
     */
    public boolean readBoundary() throws MalformedStreamException {
        byte[] marker = new byte[2];
        boolean nextChunk = false;

        head += boundaryLength;
        try {
            marker[0] = readByte();
            marker[1] = readByte();
            if (arrayequals(marker, STREAM_TERMINATOR, 2)) {
                nextChunk = false;
            } else if (arrayequals(marker, FIELD_SEPARATOR, 2)) {
                nextChunk = true;
            } else {
                throw new MalformedStreamException("Unexpected characters follow a boundary");
            }
        } catch (IOException e) {
            throw new MalformedStreamException("Stream ended unexpectedly");
        }
        return nextChunk;
    }

    /**
     * <p>Changes the boundary token used for partitioning the stream.</p>
     * <p>
     * <p>This method allows single pass processing of nested multipart streams.</p>
     * <p>
     * <p>The boundary token of the nested stream is <code>required</code> to be of the same length as the boundary token
     * in parent stream.</p>
     * <p>
     * <p>Restoring the parent stream boundary token after processing of a nested stream is left to the application.</p>
     *
     * @param boundary The boundary to be used for parsing of the nested stream.
     * @throws IllegalBoundaryException if the <code>boundary</code> has a different length than the one being currently
     *                                  parsed.
     */
    public void setBoundary(byte[] boundary) throws IllegalBoundaryException {

        if (boundary.length != boundaryLength - BOUNDARY_PREFIX.length) {
            throw new IllegalBoundaryException("The length of a boundary token can not be changed");
        }

        System.arraycopy(boundary, 0, this.boundary, BOUNDARY_PREFIX.length, boundary.length);
    }

    /**
     * <p>Reads the <code>header-part</code> of the current <code>encapsulation</code>.</p>
     * <p>
     * <p>Headers are returned verbatim to the input stream, including the trailing <code>CRLF</code> marker. Parsing is
     * left to the application.</p>
     *
     * @return The <code>header-part</code> of the current encapsulation.
     * @throws MalformedStreamException if the stream ends unexpecetedly.
     */
    public String readHeaders() throws MalformedStreamException {
        int i = 0;
        byte b;
        // to support multi-byte characters
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        int size = 0;
        while (i < HEADER_SEPARATOR.length) {
            try {
                b = readByte();
            } catch (IOException e) {
                throw new MalformedStreamException("Stream ended unexpectedly");
            }
            if (++size > HEADER_PART_SIZE_MAX) {
                throw new MalformedStreamException("Header section has more than " + HEADER_PART_SIZE_MAX
                        + " bytes (maybe it is not properly terminated)");
            }
            if (b == HEADER_SEPARATOR[i]) {
                i++;
            } else {
                i = 0;
            }
            baos.write(b);
        }

        String headers = null;
        if (headerEncoding != null) {
            try {
                headers = baos.toString(headerEncoding);
            } catch (UnsupportedEncodingException e) {
                // fall back to platform default if specified encoding is not supported.
                headers = baos.toString();
            }
        } else {
            headers = baos.toString();
        }

        return headers;
    }

    /**
     * <p>Reads <code>body-data</code> from the current <code>encapsulation</code> and writes its contents into the output
     * <code>Stream</code>.</p>
     * <p>
     * <p>Arbitrary large amounts of data can be processed by this method using a constant size buffer.</p>
     *
     * @param output The <code>Stream</code> to write data into. May be null, in which case this method is equivalent to
     *               {@link #discardBodyData()}.
     * @return the amount of data written.
     * @throws MalformedStreamException if the stream ends unexpectedly.
     * @throws IOException              if an i/o error occurs.
     */
    public int readBodyData(OutputStream output) throws MalformedStreamException, IOException {
        final InputStream istream = newInputStream();
        return (int) Streams.copy(istream, output, false);
    }

    /**
     * Creates a new {@link ItemInputStream}.
     *
     * @return A new instance of {@link ItemInputStream}.
     */
    protected ItemInputStream newInputStream() {
        return new ItemInputStream();
    }

    /**
     * <p>Reads <code>body-data</code> from the current <code>encapsulation</code> and discards it.</p>
     * <p>
     * <p>Use this method to skip encapsulations you don't need or don't understand.</p>
     *
     * @return The amount of data discarded.
     * @throws MalformedStreamException if the stream ends unexpectedly.
     * @throws IOException              if an i/o error occurs.
     */
    public int discardBodyData() throws MalformedStreamException, IOException {
        return readBodyData(null);
    }

    /**
     * Finds the beginning of the first <code>encapsulation</code>.
     *
     * @return <code>true</code> if an <code>encapsulation</code> was found in the stream.
     * @throws IOException if an i/o error occurs.
     */
    public boolean skipPreamble() throws IOException {

        // first delimiter may be not preceded with a CRLF.
        System.arraycopy(boundary, 2, boundary, 0, boundary.length - 2);
        boundaryLength = boundary.length - 2;
        try {
            // discard all data up to the delimiter.
            discardBodyData();

            // read boundary - if succeded, the stream contains an encapsulation.
            return readBoundary();
        } catch (MalformedStreamException e) {
            return false;
        } finally {
            // restore delimiter.
            System.arraycopy(boundary, 0, boundary, 2, boundary.length - 2);
            boundaryLength = boundary.length;
            boundary[0] = CR;
            boundary[1] = LF;
        }
    }

    /**
     * Compares <code>count</code> first bytes in the arrays <code>a</code> and <code>b</code>.
     *
     * @param a     The first array to compare.
     * @param b     The second array to compare.
     * @param count How many bytes should be compared.
     * @return <code>true</code> if <code>count</code> first bytes in arrays <code>a</code> and <code>b</code> are
     * equal.
     */
    public static boolean arrayequals(byte[] a, byte[] b, int count) {
        for (int i = 0; i < count; i++) {
            if (a[i] != b[i]) {
                return false;
            }
        }
        return true;
    }

    /**
     * Searches for a byte of specified value in the <code>buffer</code>, starting at the specified
     * <code>position</code>.
     *
     * @param value The value to find.
     * @param pos   The starting position for searching.
     * @return The position of byte found, counting from beginning of the <code>buffer</code>, or <code>-1</code> if not
     * found.
     */
    protected int findByte(byte value, int pos) {
        for (int i = pos; i < tail; i++) {
            if (buffer[i] == value) {
                return i;
            }
        }

        return -1;
    }

    /**
     * Searches for the <code>boundary</code> in the <code>buffer</code> region delimited by <code>head</code> and
     * <code>tail</code>.
     *
     * @return The position of the boundary found, counting from the beginning of the <code>buffer</code>, or
     * <code>-1</code> if not found.
     */
    protected int findSeparator() {
        int first;
        int match = 0;
        int maxpos = tail - boundaryLength;
        for (first = head; (first <= maxpos) && (match != boundaryLength); first++) {
            first = findByte(boundary[0], first);
            if (first == -1 || (first > maxpos)) {
                return -1;
            }
            for (match = 1; match < boundaryLength; match++) {
                if (buffer[first + match] != boundary[match]) {
                    break;
                }
            }
        }
        if (match == boundaryLength) {
            return first - 1;
        }
        return -1;
    }

    /**
     * Thrown to indicate that the input stream fails to follow the required syntax.
     */
    @SuppressWarnings("serial")
    public static class MalformedStreamException extends IOException {

        /**
         * Constructs a <code>MalformedStreamException</code> with no detail message.
         */
        public MalformedStreamException() {
            super();
        }

        /**
         * Constructs an <code>MalformedStreamException</code> with the specified detail message.
         *
         * @param message The detail message.
         */
        public MalformedStreamException(String message) {
            super(message);
        }
    }

    /**
     * Thrown upon attempt of setting an invalid boundary token.
     */
    @SuppressWarnings("serial")
    public static class IllegalBoundaryException extends IOException {

        /**
         * Constructs an <code>IllegalBoundaryException</code> with no detail message.
         */
        public IllegalBoundaryException() {
            super();
        }

        /**
         * Constructs an <code>IllegalBoundaryException</code> with the specified detail message.
         *
         * @param message The detail message.
         */
        public IllegalBoundaryException(String message) {
            super(message);
        }

    }

    /**
     * An {@link InputStream} for reading an items contents.
     */
    public class ItemInputStream extends InputStream implements Closeable {

        /* The number of bytes, which have been read so far */
        private long total;

        /* The number of bytes, which must be hold, because they might be a part of the boundary */
        private int pad;

        /* The current offset in the buffer */
        private int pos;

        /* Whether the stream is already closed. */
        private boolean closed;

        /**
         * Creates a new instance.
         */
        ItemInputStream() {
            findSeparator();
        }

        /**
         * Called for finding the separator.
         */
        private void findSeparator() {
            pos = MultipartReader.this.findSeparator();
            if (pos == -1) {
                if (tail - head > keepRegion) {
                    pad = keepRegion;
                } else {
                    pad = tail - head;
                }
            }
        }

        /**
         * Returns the number of bytes, which have been read by the stream.
         *
         * @return Number of bytes, which have been read so far.
         */
        public long getBytesRead() {
            return total;
        }

        /**
         * Returns the number of bytes, which are currently available, without blocking.
         *
         * @return Number of bytes in the buffer.
         * @throws IOException An I/O error occurs.
         */
        public int available() throws IOException {
            if (pos == -1) {
                return tail - head - pad;
            }
            return pos - head;
        }

        /* Offset when converting negative bytes to integers */
        private static final int BYTE_POSITIVE_OFFSET = 256;

        /**
         * Returns the next byte in the stream.
         *
         * @return The next byte in the stream, as a non-negative integer, or -1 for EOF.
         * @throws IOException An I/O error occurred.
         */
        public int read() throws IOException {
            if (closed) {
                throw new IOException("The stream is closed.");
            }
            if (available() == 0) {
                if (makeAvailable() == 0) {
                    return -1;
                }
            }
            ++total;
            int b = buffer[head++];
            if (b >= 0) {
                return b;
            }
            return b + BYTE_POSITIVE_OFFSET;
        }

        /**
         * Reads bytes into the given buffer.
         *
         * @param b   The destination buffer, where to write to.
         * @param off Offset of the first byte in the buffer.
         * @param len Maximum number of bytes to read.
         * @return Number of bytes, which have been actually read, or -1 for EOF.
         * @throws IOException An I/O error occurred.
         */
        public int read(byte[] b, int off, int len) throws IOException {
            if (closed) {
                throw new IOException("The stream is closed.");
            }
            if (len == 0) {
                return 0;
            }
            int res = available();
            if (res == 0) {
                res = makeAvailable();
                if (res == 0) {
                    return -1;
                }
            }
            res = Math.min(res, len);
            System.arraycopy(buffer, head, b, off, res);
            head += res;
            total += res;
            return res;
        }

        /**
         * Closes the input stream.
         *
         * @throws IOException An I/O error occurred.
         */
        public void close() throws IOException {
            close(false);
        }

        /**
         * Closes the input stream.
         *
         * @param pCloseUnderlying Whether to close the underlying stream (hard close).
         * @throws IOException An I/O error occurred.
         */
        public void close(boolean pCloseUnderlying) throws IOException {
            if (closed) {
                return;
            }
            if (pCloseUnderlying) {
                closed = true;
                input.close();
            } else {
                for (; ; ) {
                    int av = available();
                    if (av == 0) {
                        av = makeAvailable();
                        if (av == 0) {
                            break;
                        }
                    }
                    skip(av);
                }
            }
            closed = true;
        }

        /**
         * Skips the given number of bytes.
         *
         * @param bytes Number of bytes to skip.
         * @return The number of bytes, which have actually been skipped.
         * @throws IOException An I/O error occurred.
         */
        public long skip(long bytes) throws IOException {
            if (closed) {
                throw new IOException("The stream is closed.");
            }
            int av = available();
            if (av == 0) {
                av = makeAvailable();
                if (av == 0) {
                    return 0;
                }
            }
            long res = Math.min(av, bytes);
            head += res;
            return res;
        }

        /**
         * Attempts to read more data.
         *
         * @return Number of available bytes
         * @throws IOException An I/O error occurred.
         */
        private int makeAvailable() throws IOException {
            if (pos != -1) {
                return 0;
            }

            // move the data to the beginning of the buffer
            total += tail - head - pad;
            System.arraycopy(buffer, tail - pad, buffer, 0, pad);

            // refill buffer with new data
            head = 0;
            tail = pad;

            for (; ; ) {
                int bytesRead = input.read(buffer, tail, bufSize - tail);
                if (bytesRead == -1) {
                    // the last pad amount is left in the buffer
                    // boundary can't be in there so signal an error condition.
                    final String msg = "Stream ended unexpectedly";
                    throw new MalformedStreamException(msg);
                }

                tail += bytesRead;

                findSeparator();
                int av = available();

                if (av > 0 || pos != -1) {
                    return av;
                }
            }
        }

        /**
         * Returns, whether the stream is closed.
         *
         * @return true, if the stream is closed, otherwise false.
         */
        public boolean isClosed() {
            return closed;
        }
    }
}
